In fatigue, pathological fatigue and physiological fatigue are known, and it is said that the pathological fatigue which is observed while being ill or performing excessive exercise is associated with an increase in the blood ammonia level. On the other hand, in physiological fatigue in normal subjects, an increase in the blood ammonia level is not observed.
Further, as the method for assessing feelings of fatigue, i.e., subjective symptoms of fatigue, a method using the table for assessing subjective symptoms (Non-patent document 1) made by the Industrial Fatigue Research Committee belonging to the Japan Society for Occupational Health is known. According to the table for assessing subjective symptoms, feelings of fatigue are classified into three factors, which are considered as follows: “drowsiness and dullness” (Group 1), “difficulty in concentration” (Group 2), and “physical discomfort” (Group 3).
Ornithine is used, mostly in the U.S. and Japan, as a food material to strengthen muscle formation through secretion of growth hormone or to prevent obesity by enhancing basal metabolism. Further, ornithine is used in the form of L-ornithine-L-aspartate as a medicament used to improve a liver disorder in Europe.
It is known that in pathological fatigue associated with an increase in the blood ammonia level, by administering ornithine or a salt thereof, the blood ammonia level is lowered thereby to relive the pathological fatigue (Patent documents 1 to 3 and Non-patent document 2). However, it is not known that feelings of fatigue, i.e., subjective symptoms of fatigue in physiological fatigue in normal subjects are relieved by ornithine or a salt thereof.
Patent document 1: Japanese Published Examined Patent Application No. 7767/1967
Patent document 2: Japanese Published Examined Patent Application No. 3194/1971
Patent document 3: Japanese Published Examined Patent Application No. 8592/1966
Non-patent document 1: Hirou no Sokutei to Hyoka (Determination and Evaluation of Fatigue)
Non-patent document 2: “Arzneim.-Forsch (Drug Res.)”, Vol. 8, pp. 1064-1067, 1970